A slow page is not rebuilt twice more for being slow

The deploy builds per sha and never cancels, deliberately: sharing a concurrency
group put every run in `waiting` until the next push swept it, and no image was
pushed at all. The cost of that correctness is that a burst of pushes runs
several full 6,099-page builds at once on one box.

Under that contention pages cross the 60-second default and are RETRIED —
measured on a five-build burst, /docs/console, /docs/credits and /docs/enso each
failed "attempt 1 of 3" while the run was two-thirds through its pages. A retry
does not make a contended page faster. It makes the same page cost three times,
on the box that was already the constraint.

Three minutes is well above what any page here takes with the box to itself, so
the normal path is unchanged; only the pathological one stops multiplying.

apps/docs/next.config.ts

@@ -79,6 +79,21 @@ const config: NextConfig = {
   // HTTP redirects live in public/_redirects (Cloudflare Pages). This site
   // deploys as a static export (`out/`), which ignores next.config redirects(),
   // so declaring them here would be dead config.
+  // A page gets three minutes, not the default one.
+  //
+  // The deploy workflow builds PER SHA and never cancels — deliberately, because
+  // sharing a group meant every run sat in `waiting` until the next push swept
+  // it and no image was ever pushed. The cost of that correctness is that a
+  // burst of pushes runs several full 6,099-page builds at once on one box, and
+  // under that contention pages cross 60s and are RETRIED: measured on a
+  // five-build burst, /docs/console, /docs/credits and /docs/enso each failed
+  // "attempt 1 of 3" while the run was only two-thirds through its pages.
+  //
+  // A retry does not make a contended page faster; it makes the same page cost
+  // three times. Three minutes is above what any page here takes when a build
+  // has the box to itself, so on the normal path this changes nothing at all —
+  // it only stops a slow page being rebuilt twice more for being slow.
+  staticPageGenerationTimeout: 180,
   experimental: {
     // Reduce peak memory during webpack compilation for large builds.
     webpackMemoryOptimizations: true,